This invention pertains to light amplification systems, particularly to those utilizing light intensifier tubes.
Light intensifier tubes of a great variety of designs have long been known and used in various military and civil applications requiring the viewing or photographing of a scene that is illuminated inadequately for viewing with the naked eye or with ordinary optical systems. The typical light intensifier tube, however, cannot amplify light as much as many purposes require. The conventional solution of this problem is to cascade several intensifier tubes to obtain the necessary gain, which may be as large as 100,000 to 1. A cascade of light intensifier tubes, however, has the drawback of being very expensive.
If the light intensifier tubes used employ electrostatic lens focusing, a cascade has a further disadvantage. The phosphor screen (output) of each tube must be held at a fixed electrical potential (e.g. 15 kV) above the photocathode (input) of the tube; furthermore, the phosphor screen of each tube must be at the same potential as the photocathode of the next tube of the cascade, with which it is in physical contact. Thus, the phosphor screen of the third tube in a cascade must be at a very high voltage, e.g. 45 kV, above the photocathode of the first tube in the cascade. This, obviously, requires a relatively large and expensive power supply.
The present inventions use an optical feedback system to reduce the number of cascaded light intensifier tubes required. Feedback systems to be used in conjunction with light amplification systems are known, e.g. U.S. Pat. No. 3,154,687, issued to Perl et al. One problem encountered in the design of an optical feedback system is the very serious one of registering the fed-back image with the original input more-or-less perfectly. If this problem is neither solved nor avoided, the resultant output image will be blurred.
It is the primary purpose of the present invention to overcome these disadvantages of light amplification systems involving a cascade of light intensifier tubes and the problems associated with conventional optical feedback systems.